Dinh Hong Minh has just repaired 2 problems ( 1074,1097 )
for you :

   - 1074
           +  when s='', you call s[1] = '-' --> crash;
           +  Use {$R+} in the begining of source code to
solved other error.

   - 1097
           + The initialize value of Max is 1, you use 0 ---
--> wrong answer.
           + Your algo is too slow, you must change it.

@ Good luck !!!

PS : Can you tell him the way to solve 1018 ?
     Mail to : dinhhongminh@yahoo.com